This invention relates to a caster which is provided with a damping mechanism and which is mounted on a wheelchair or the like.
A prior art caster for absorbing shocks comprises a bracket which is connected to a body, a link which is connected to rotate with the bracket and which supports a wheel, and a cushioning which is interposed between the bracket and the link.
However the carrying load and shock-absorbing efficiency of this type of caster are determined by the resilient characteristics of the cushioning rubber. As a result, the problem has arisen that the effectiveness of an initial movement is reduced if the cushioning rubber is too hard. Conversely metal contact may result if the cushioning rubber is too soft.
The caster is provided with a metal spring has resulted in the problem that the size of the caster is increased and thus it is difficult to assemble this type of caster into the wheelchair currently in use.
This invention has the object of providing a caster which solves the above problems.
In order to solve the above problems, this invention provides a caster comprising a bracket which is connected with a body of a vehicle, a link which is connected with the bracket rotatably, a wheel which is connected with the link rotatably, and a compressible rubber block which deforms according to the rotation of the link, wherein the compressible rubber block has an initial compressible part which partially decreases a cross section of the compressible rubber block. As a result, the compressible rubber block can smooth out the rotation of the link and restrain input forces on the body by the initial compressible part deforming with respect to an initial input force on the wheels.
When a large input force is applied on the wheels, the input force on the body is restrained by limiting the rotation range of the link which thus prevents metal contact comprising the link making direct contact with the bracket etc. This is enabled by the deformation of sections other than the initial compressible part after the initial compressible part has deformed.
A torsional rubber bush is disposed co-axially to the rotational axis of the link and a compressible rubber block is disposed between the bracket and the link. As a result, the size of the caster can be made reduced.
The initial compressible rubber block is made a cylindrical shape and a part of the cylindrical compressible rubber block is formed a cone shape which has a reduced cross section. As a result, when the compressible rubber block is compressed, deformation begins from the initial compressible part which has a smaller cross section. Thereafter the elastic recovery force rapidly increases due to the fact that conical parts deform from the side which has the smaller cross section together with increases in the degree of deformation. The conical parts are positioned to sandwich the initial compressible part.
The compressible rubber block has a cylindrical shape and at least a part of the cylindrical compressible rubber block as the initial compressible part is formed so that a cross section of the part is smaller than other parts. As a result, when the compressible rubber block is compressed, firstly deformation begins from the initial compressible part which has a smaller cross section. Thereafter the elastic recovering force rapidly increases due to the fact that each large diameter part which sandwiches the initial compressible part undergoes deformation. In this manner, shocks on the wheel from the road surface are effectively absorbed and input forces on the body can be restrained by preventing metal contact resulting from the link coming into contact with the bracket.
A retainer is provided at periphery of the compressible rubber block, and the retainer come into contact with a member supporting the compressible rubber block according to the deformation of the initial compressible part. As a result, when the compressible rubber block is compressed, it is compressed firstly from the initial compressible part which has a smaller cross section and the retainer abuts with the a member which supports the initial compressible part. As a result, the elastic recovering force is rapidly increased. In this manner, shocks on the wheel from the road surface are effectively absorbed and input forces to the vehicle body can be restrained by preventing metal contact due to the link coming into contact with the bracket.
Annular spacers are respectively provided at the top side and bottom side of the compressible rubber block, a maximum amount of compression of the compressible rubber block is determined by which the respective spacers contacts as the deformation of the compressible rubber block. Therefore the compression ratio of the compressible rubber block can be limited by the contact between the spacers. Therefore it is possible to accurately control the amount of stroke of the casters and therefore restrain individual differences in damping performance resulting from differences quality in the manufacture of the compressible rubber blocks.
The annular spacer has a height regulation member which enables a maximum amount of compression of the compressible rubber block to be varied. Therefore it is possible to vary the amount of stroke of the caster in a simple manner.
The cross section of the initial compressible rubber block is gradually decreased toward a top of the compressible rubber block to a deformation direction of the compressible rubber block, annular spacers are respectively provided at the top side and bottom side of the compressible rubber block and the respective spacers contacts with the initial compressible rubber block according to the deformation of the compressible rubber block. Therefore as the initial compressible section is compressed, the end of the block abuts with the end face of the spacer. As a result, when the compressible rubber block is compressed, deformation begins from the initial compressible part which has a smaller surface area. Therefore the input forces on the vehicle body can be restrained by smoothing out the rotation of the link. When a large input force is applied to the vehicle wheels, the initial compressible part of the compressible rubber block comes into contact with the end face of the spacer. Therefore the elastic recovering force of the compressible rubber block increases sharply. As a result, it is possible to restrain input forces on the vehicle body by limiting the rotation range of the link.
A torsional rubber bush as the compressible rubber block is provided which deforms to a torsion direction as the link rotates As a result, the torsional rubber cushion forms a torsion in response to loads on the vehicle body to determine the inclination of the link. The compressible rubber block is compressed in response to input forces on the vehicle wheels and swing in the link is damped. Thus it is possible to set the load bearing characteristics and damping characteristics of the caster on the basis of variations in the hardness or shape of the torsional rubber bush and the compressible rubber block.